Add a platform specific configuration checker

For each platform, we may need to perform some basic checks to see
that available tools perform as we expect them.

For the moment, the added checkers test that Perl gives the expected
path format.  This should help MingW users to see if they run an
appropriate Perl implementation, for example.
Reviewed-by: NAndy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2851)

Configurations/unix-checker.pm

+#! /usr/bin/perl
+
+use Config;
+
+# Check that the perl implementation file modules generate paths that
+# we expect for the platform
+use File::Spec::Functions qw(:DEFAULT rel2abs);
+
+if (rel2abs('.') !~ m|/|) {
+    die <<EOF;
+
+******************************************************************************
+This perl implementation doesn't produce Unix like paths (with forward slash
+directory separators).  Please use an implementation that matches your
+building platform.
+
+This Perl version: $Config{version} for $Config{archname}
+******************************************************************************
+EOF
+}
+
+1;

Configurations/windows-checker.pm

+#! /usr/bin/perl
+
+use Config;
+
+# Check that the perl implementation file modules generate paths that
+# we expect for the platform
+use File::Spec::Functions qw(:DEFAULT rel2abs);
+
+if (rel2abs('.') !~ m|\\|) {
+    die <<EOF;
+
+******************************************************************************
+This perl implementation doesn't produce Windows like paths (with backward
+slash directory separators).  Please use an implementation that matches your
+building platform.
+
+This Perl version: $Config{version} for $Config{archname}
+******************************************************************************
+EOF
+}
+
+1;

Configure

@@ -993,6 +993,25 @@ $target{build_scheme} = [ $target{build_scheme} ]
 my ($builder, $builder_platform, @builder_opts) =
     @{$target{build_scheme}};
 
+foreach my $checker (($builder_platform."-".$target{build_file}."-checker.pm",
+                      $builder_platform."-checker.pm")) {
+    my $checker_path = catfile($srcdir, "Configurations", $checker);
+    if (-f $checker_path) {
+        my $fn = $ENV{CONFIGURE_CHECKER_WARN}
+            ? sub { warn $@; } : sub { die $@; };
+        if (! do $checker_path) {
+            if ($@) {
+                $fn->($@);
+            } elsif ($!) {
+                $fn->($!);
+            } else {
+                $fn->("The detected tools didn't match the platform\n");
+            }
+        }
+        last;
+    }
+}
+
 push @{$config{defines}}, "NDEBUG"    if $config{build_type} eq "release";
 
 if ($target =~ /^mingw/ && `$target{cc} --target-help 2>&1` =~ m/-mno-cygwin/m)